Lamps of such kind have a discharge vessel filled with a discharge medium, for example an inert gas—with or without added mercury and possibly other fill additives. Arranged mutually opposite inside the discharge vessel are two electrodes each supported by a lamp shaft arranged coaxially relative to the respective electrode. Also provided in the lamp shaft is a gas-tight electricity passage for the electric connection between external power terminals and the electrodes. That sealed section of the lamp shaft can be produced using, for example, transition glasses (being then known as a graded seal). Other lamp-sealing technologies, for example foil sealing or foil pinching, are however also employed for lamps of such kind.
Particularly in the case of high-power lamps in, say, the kilowatt or multi-kilowatt range, arranging the electrodes such as to be permanently gas-tight is challenging owing to their increasing mass. Even while lamps of such kind are being transported, vibrations due to shock impacts can occur on the electrode rods supporting the massive electrode heads and may cause damage to the lamp shaft resulting in premature seal or lamp breakage. That problem will be further exacerbated on the anode-side lamp shaft of a lamp provided for direct current (DC) because the anode has to be implemented as particularly massive. Added to this is the fact that the electrode rods needed for the massive electrode heads are subjected to a relatively high stress owing to the change in temperature during the startup phase or when the lamp has been switched off. That complicates centering and guiding the electrode rods because mechanical transmission of forces and/or stresses onto the lamp shafts has to be prevented. Stress breaks could otherwise occur.
Document WO 2008/006759 discloses a short-arc discharge lamp in which the electrode rods are centered and/or guided with the aid of a narrow section in the lamp shafts. The narrow section surrounds the electrode rod closely but not tightly. Any vibrations in the electrode rod occurring when the lamp is shaken, for example during transportation, may consequently be transmitted to the narrow section and cause damage (natural resonance). Varying temperature-related expansion which the electrode rod undergoes can furthermore result in rubbing in the narrow section against the inner wall of the lamp shaft and in said shaft's being damaged as a result.